TF2 is my all time favorite game... But slapping mechanics from one good game onto another game isn't a recipe for a good idea. I think it's very important to the balance of MB2 Open that there are no healers. Even though I played TF2 Medic competitively for a while, I don't want a healer in open. And I certainly don't want a Spy class, Jedi with Mind Trick is enough stealth.
Engineer classes are really hard to do right. TF2 Engineer is a great balance of requiring a lot of resource management and thought (unless your team stacks the class), and the buildings have lots of counter play. Compare this to Overwatch 1 Season 1 Torbjorn, which was a braindead awful class. It's all in the nuance of execution that can make a builder class from a cool niche to an awful noob trap. And most game designers make turret classes really annoying.
There are aspects of MB2 that would make turrets more annoying to deal with. Firstly, it's lack of splash damage. There's explosives in the game but most are very resource limited. There's no Soldier or Demoman equivalent in MB2. The MB2 classes with nades have very limited uses, and the classes with rockets cannot move while firing the rocket, which is critical because in TF2 you deal with sentries by peaking around a corner to fire a rocket then going back into cover.
The one idea from TF2 I'd really like to see in MB2 is a character with explosive projectiles as a primary (and can move while firing them), but the explosions will be weaker as in they don't knock you down and they don't do insane damage. This type of weapon is easy to learn, hard to master, which I think is great from a design standpoint. I suggested something like this in my unironic Gungan proposal which is built around the Booma inspired by the TF2 Demoman's grenade launcher.